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S.C.A.R. 1000 (single coil assult rifle 1000j)

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LAN_403

PSCG

Tue Nov 22 2011, 08:56PM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
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Posts: 136

I meant how are you are switching on your SCR (the word "topology" was unfortunate to describe what i was thinking - sorry), but i can see it now from the schematic you posted.

ben5017

Tue Nov 22 2011, 09:33PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
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Posts: 156

Does the schematic look alright?

PSCG

Wed Nov 23 2011, 02:09PM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
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I think that the polarity of the thyristor (as it is designed in the schematic diagram) is the opposite. Except that, the schematic is correct.

ben5017

Wed Nov 23 2011, 04:39PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
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So just flip the scr 180 degrees? Should I use more than 4.2 volt gate trigger?

PSCG

Wed Nov 23 2011, 05:19PM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
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Only change the thyristor's polarity on your schematic. If you have managed to trigger your SCR successfuly, then you don't need to change something.

For what voltage is the thyristor's gate rated (at what voltage it turns fully on)?

Sorry for causing misunderstaning to you. English is not my native language.....

ben5017

Thu Nov 24 2011, 02:00AM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
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finally got the first couple shots outta her. everything seems to be working great with only warm temps on the coil and charging circute. only problem is my voltmeter. it says -1 volt while the charger is on.. when i turn the charger off it reads the right voltrage? this is a problem because i have to manualy turn the charger of when disired voltage is reached. there is no automatic shut off.. any thoughts?

pscg: you were right i had the scr the wrong way!

thanks guys this is a big miolestone in this 3 month project and i deff appreciate the help

Inducktion

Mon Nov 28 2011, 04:50PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

- 1.... doesn't that mean overload?

Southern Borg

Mon Nov 28 2011, 08:33PM

Registered Member #4235 Joined: Mon Nov 28 2011, 10:57AM
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Ben, that's a wicked looking gun. Well done mate!

Couple of things it might help to know...

First, you really need to gently charge up the capacitors before using them "flat out". The chinese caps are ALL crap, and they nearly all come out of the cap-making machine without being properly "formed" - this means they're virgins! You need to 'break them in'. Sounds crazy, I know, but trust me - you won't lose as many, and they'll be much more reliable. (Don't worry, I bought the chinese caps too - that's how I know! :()

If you can get your hands on a variable DC power supply, all you do is hook them up (all in parallel is fine), then slowly increase the voltage bit by bit, let it stabilise for a minute or so, then increase it a bit more, until you've reached the limit of the power supply or the caps. This helps to fix the chemical oxide inside them to the metal. It only takes a half hour or so, and it's well worth the effort. It also reduces the ESR, which is like a resistance inside the caps themselves. You'll get bigger bang for your buck. (Out of the muzzle, I mean, not another cap explosion!!!)

You can still do that now, if you have access to a power supply. It might help prevent another explosion.

Second, you REALLY need a better multimeter. If you can send me your details (by private message is best), I'll pack up an old DMM I'm not using any more and post it off to you. It's not a gold-plated Fluke (it's actually a Digitech QM1250 if that helps), but it will check your SCRs and diodes and measure your resistance much more reliably than what you're using now, plus it's rated for high voltage (1000V+). Why? Because someone did the same for me when I was starting out 35 years ago, and I know how it feels to have less than the best tools. Plus - hell, that's a nice design - you've given me a reason to keep on with my own coilgun!

Third, just for the future : get yourself a decent soldering iron. It should have adjustable temperature, be rated at at LEAST 40W, and should feel comfortable in your hand. That will make soldering so much easier, you won't believe it! You can get these from various places - Fry's, Radio Shack, Jaycar (they have US outlets, I believe) or just a local hobbyist store if one's close. You can also try eBay, but they tend to flog real crap. I got a Fenle 859AD for about $200 about 18 months ago off eBay, but I ended up using my own iron with the Fenle controller. You'd be looking at about $120 for a really nice soldering station, but it will repay itself over and over again, trust me!

I noticed your last post, with the deflenegrated cap (I just made up that word ;)). It sounds like either the diode broke (test it with your multimeter - if it's broke, it will read either open circuit or short circuit both ways), or the caps are really dodgy. I'd suggest not charging them up to too high a voltage - keep it at 200-250V for now, until you're sure the other caps are OK. You'll need to clean the other caps if one of them blew - use LOTS of water to wash the liquid off the other caps and the solder joints, or it will eat into them and your wiring. Nasty stuff. Dry everything out, and check to see no other caps are bulging or leaking before you power up again, just to be sure!

I hope this helps. Let me know if you can use the DMM.

Cheers,
Pete

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